Imperial College London

Dr Koon-Yang Lee

Faculty of EngineeringDepartment of Aeronautics

Professor in Polymer Engineering



+44 (0)20 7594 5150koonyang.lee




325City and Guilds BuildingSouth Kensington Campus





Publication Type

105 results found

Mohammed A, Gaduan A, Chaitram P, Pooran A, Lee K-Y, Ward Ket al., 2023, Sargassum inspired, optimized calcium alginate bioplastic composites for food packaging, Food Hydrocolloids, Vol: 135, Pages: 1-12, ISSN: 0268-005X

Plastic pollution, more specifically from food packaging and containers which account for the largest share of 36% of current plastic production, is one of the greatest threats to the natural environment and human health. Thus, the development of alternative renewable plastics are needed to complement a circular economy and reduce resource depletion. Seaweeds have been known to possess good film forming properties ideal for bioplastic production, and Sargassum natans-an invasive brown seaweed which has been inundating the shores of the Caribbean, has been shown to be an excellent candidate. This study presents, for the first time, the development of a novel optimized biodegradable alginate composite bioplastic as an alternative to traditional plastic packaging. The optimization process was carried out using Response Surface Methodology (RSM) resulting in a formulation of 6 wt% alginate, 0.263 wt% starch, 0.35 wt% CMC, 0.065 g/g sorbitol and 0.025 g/g PEG 200- with ultra-high oxygen barrier (OP - 0.2 cm3 μm m−2 d−1 kPa−1), good water vapor barrier (WVP - 2.18 × 10−12 g m/m2 s Pa) and high tensile modulus ( - 3.93 GPa)- with no migration of additives into a simulated aqueous food system in 10 days. Furthermore, composite films were found to fully degrade in 14 days and possessed better OP, higher WVP and comparable material properties to HDPE, PET and PLA. Ultimately, our results support alginate composite films as a viable alternative for food packaging best fitted for low moisture environments-encouraging the use of renewable materials for packaging innovation and supporting UNSDGs.

Journal article

Gaduan AN, Li J, Hill G, Wallis C, Burgstaller C, Lee K-Yet al., 2023, Simulating the recycling of milk bottles in the UK: Influence of blending virgin and repeatedly melt-extruded high-density polyethylene, Resources, Conservation and Recycling, Vol: 189, Pages: 1-8, ISSN: 0921-3449

The UK Dairy Roadmap has set a target of achieving 50 wt.-% high density polyethylene (HDPE) recyclate in their HDPE milk bottles. Such high recyclate content will lead to the accumulation of HDPE recyclates that have been subjected to different number of melt extrusion cycles in the supply chain. This work investigates the structure-property relationship of blending virgin HDPE (vHDPE) with these different grades of repeatedly melt-extruded HDPE (rHDPE). HDPE was subjected to 10, 20 and 50 melt-extrusion cycles and blended with vHDPE. No significant difference in terms of melt rheology, tensile properties and overall migration in acidic and aqueous environments of the blends of the different rHDPEs with vHDPE was observed when compared to vHDPE. This study demonstrates the feasibility of blending up to 50 wt.-% rHDPE of different grades with vHDPE as set out in the UK Dairy Roadmap.

Journal article

Caro-Astorga J, Lee K, Ellis T, 2022, Increasing bacterial cellulose compression resilience with glycerol or PEG400 as a route to more robust engineered living materials, Carbohydrate Polymer Technologies and Applications, Vol: 4, Pages: 1-6, ISSN: 2666-8939

Bacterial cellulose (BC) is one of the current natural materials at the edge of innovation in engineered living materials (ELMs) research due to its ease of growth and outstanding properties as a hydrogel. One of the main limitations of this material, however, is its quick dehydration in open environments as water molecules leave the porous network. Here we show that other solvents with higher evaporation temperatures, namely glycerol and polyethylene glycol (PEG), can play the same role as water within the BC structure interacting with cellulose fibres via hydrogen bonds. We demonstrate that these molecules provide up to a 130-fold improvement in the Young´s Modulus of BC hydrogels to compression forces in a concentration dependent manner. To take advantage of these effects for application in BC-based ELMs produced by Komagataeibacter rhaeticus, we also explored the effect of glycerol and PEG400 on the survival of the BC-producing bacteria in BC pieces. PEG400 at 20% doubled the material resilience to compression forces, still allowing bacteria to survive within the material for weeks. These results open further opportunities to explore new applications and stacked storage conditions.

Journal article

von Goetze R, Aljaber A, Lee K-Y, Hill G, Wallis C, Britovsek GJPet al., 2022, Towards degradable polyethylene: end-functionalised polyethylene (PE-X) and PE-I/LDPE blends from iron-catalysed chain growth of ZnEt2 with ethylene, Polymer Chemistry, Vol: 13, Pages: 6377-6385, ISSN: 1759-9954

A series of end-functionalised polyethylene materials (PE-X) has been prepared via the catalysed chain growth (CCG) reaction of diethyl zinc with ethylene, catalysed by a bis(imino)pyridine iron catalyst activated by MAO. This CCG catalyst system enables the in situ formation of long alkyl chain zinc species Zn(PE)2, which are subsequently quenched to form PE-X. Quenching with oxygen results in PE-OH, but the functionalisation appears to be limited to approximately 80% due to the formation of mixed [ZnR(OR)]n clusters. Functionalisation with sulfur leads to polysulfides, PE-Sk-PE, whereby k is affected by temperature. Functionalisation with iodine leads to PE-I with high conversion, but the degree of functionalisation appears to be chain length dependant. PE-I has been blended with LDPE, either through solution mixing or via melt blending to give PE-I/LDPE blends with different chain lengths. Characterisation of the PE-I/LDPE blends has been carried by IR spectroscopy and thermal analysis (DSC). Surface analysis by FIB-SEM and EDX analysis up to 6 μm into the surface has shown a uniform distribution of PE-I within the LDPE matrix. The propensity of alkyl iodides to undergo photolytic cleavage makes these PE-I/LDPE materials interesting candidates for degradable PE.

Journal article

Ketola AE, Song W, Lappalainen T, Salminen K, Viitala J, Turpeinen T, Miettinen A, Lee K-Y, Ketoja JAet al., 2022, Changing the structural and mechanical anisotropy of foam-formed cellulose materials by affecting bubble-fiber interaction with surfactant, ACS Applied Polymer Materials, Vol: 4, Pages: 7685-7698, ISSN: 2637-6105

Cellulose fiber materials suitable for filtering, insulation, protective, and hygiene applications can be formed using aqueous foam as a carrier phase. The subtle fiber–bubble interaction provides a tool which can be utilized to alter both structural and mechanical material properties. Earlier model surface studies have only indicated clear surface-bubble adhesion when both the surface hydrophobicity and surface tension of the solution are high enough. In this work, we first show that for silica model surfaces these basic mechanisms are similar for both nonionic polyethylene glycol sorbitan monolaurate (Tween 20) and anionic sodium dodecyl sulfate (SDS) surfactants. In the second step, thick nonwoven materials were foam formed from hydrophilic or hydrophobic viscose fibers using small amounts of cellulose microfibers (CMFs) to form a bonding agent. There was a clear variation in structure and strength properties between the samples made using different fibers and surfactants. The partial alignment and layering of fibers in the wet foam led to anisotropy in the mechanical properties of the formed samples. Using SDS, the fiber alignment was very strong for hydrophilic fibers but was reduced for hydrophobic fibers because of stronger coupling to bubbles during structure forming, impacting the microscale fiber network. For nonionic Tween 20, in addition to surfactant adsorption on the fibers, the ethoxylated surfactant headgroups are suggested to form bridges between CMFs and other fibers, restricting fiber movements during formation. For hydrophilic fibers, this showed up as a lower in-plane compression modulus but higher transverse strength for Tween 20 compared with SDS surfactant. For hydrophobic fibers, the sensitivity of the mechanical properties on surfactant type was even stronger.

Journal article

Titirici M, Baird SG, Sparks TD, Yang SM, Brandt-Talbot A, Hosseinaei O, Harper DP, Parker RM, Vignolini S, Berglund LA, Li Y, Gao H-L, Mao L-B, Yu S-H, Diez N, Ferrero GA, Sevilla M, Szilagyi PA, Stubbs CJ, Worch JC, Huang Y, Luscombe CK, Lee K-Y, Luo H, Platts MJ, Tiwari D, Kovalevskiy D, Fermin DJ, Au H, Alptekin H, Crespo-Ribadeneyra M, Ting VP, Fellinger T-P, Barrio J, Westhead O, Roy C, Stephens IEL, Nicolae SA, Sarma SC, Oates RP, Wang C-G, Li Z, Loh XJ, Myers RJ, Heeren N, Gregoire A, Perisse C, Zhao X, Vodovotz Y, Earley B, Finnveden G, Bjorklund A, Harper GDJ, Walton A, Anderson PAet al., 2022, The sustainable materials roadmap, Journal of Physics: Materials, Vol: 5, Pages: 1-98, ISSN: 2515-7639

Over the past 150 years, our ability to produce and transform engineered materials has been responsible for our current high standards of living, especially in developed economies. However, we must carefully think of the effects our addiction to creating and using materials at this fast rate will have on the future generations. The way we currently make and use materials detrimentally affects the planet Earth, creating many severe environmental problems. It affects the next generations by putting in danger the future of the economy, energy, and climate. We are at the point where something must drastically change, and it must change now. We must create more sustainable materials alternatives using natural raw materials and inspiration from nature while making sure not to deplete important resources, i.e. in competition with the food chain supply. We must use less materials, eliminate the use of toxic materials and create a circular materials economy where reuse and recycle are priorities. We must develop sustainable methods for materials recycling and encourage design for disassembly. We must look across the whole materials life cycle from raw resources till end of life and apply thorough life cycle assessments (LCAs) based on reliable and relevant data to quantify sustainability. We need to seriously start thinking of where our future materials will come from and how could we track them, given that we are confronted with resource scarcity and geographical constrains. This is particularly important for the development of new and sustainable energy technologies, key to our transition to net zero. Currently 'critical materials' are central components of sustainable energy systems because they are the best performing. A few examples include the permanent magnets based on rare earth metals (Dy, Nd, Pr) used in wind turbines, Li and Co in Li-ion batteries, Pt and Ir in fuel cells and electrolysers, Si in solar cells just to mention a few. These materials are classified as

Journal article

Herrera N, Li J, Lee K-Y, 2022, Tough poly(ethylene glycol)-sized bacterial cellulose sheet for high impact strength laminated acrylic composites, Composites Part A: Applied Science and Manufacturing, Vol: 156, Pages: 1-8, ISSN: 1359-835X

Dried and well-consolidated sheet of bacterial cellulose (BC) nanofibrils is a material structure that possesses high modulus and strength but is also brittle, which limits its potential in various advanced composite applications. Here, we report a simple method of enhancing the toughness of BC sheet by sizing the BC nanofibrils with poly(ethylene glycol) (PEG). This hinders interfibril hornification and facilitates large-scale BC nanofibril debonding, slippage and reorientation upon deformation. The PEG-sized BC sheets show high tensile strain-at-failure and work of fracture compared to neat BC sheet. PEG-sized BC reinforced laminated acrylic composites achieve a flatwise Charpy impact strength of up to 26 kJ m−2. This is a remarkable increase over the impact strength of neat impact-modified acrylic of only 12 kJ m−2, especially when the BC loading required to achieve this radical improvement is only 0.2 wt-%. Our study opens new paradigm in using low BC loading to achieve performance improvements suitable for high value composite applications.

Journal article

Gaduan A, Singkronart K, Bell C, Tierney E, Burgstaller C, Lee K-Yet al., 2022, Mechanical upcycling immiscible polyethylene terephthalate-polypropylene blends with carbon fibre reinforcement, ACS Applied Polymer Materials, Vol: 4, ISSN: 2637-6105

Ineffective sorting of post-consumer plastics remains one of the major obstacles in the recycling of plastics. Consequently, these highly heterogeneous, mixed post-consumer plastics will end up in landfill or have to be incinerated as repurposing them directly would lead to a polymer blend with inferior quality for many end-uses. In this work, we demonstrate the use of carbon fibers (CFs) to practically upgrade the mechanical properties of mixed plastics, adding value to them. This will create a stronger demand for mixed plastics to be used in various engineering applications. Using polyethylene terephthalate (PET) and polypropylene (PP) as the model immiscible polymer blend, we showed that the incorporation of CFs increased the tensile, flexural, and single-edge notched fracture toughness of the resulting CF-reinforced PET/PP composite blends. Despite the high environmental burden associated with the production of CFs, cradle-to-grave life-cycle analysis showed that CF-reinforced PET/PP composites have a lower environmental impact than the life-cycle scenarios of “doing nothing” and repurposing immiscible PET/PP blends as it is without CF reinforcement. This can be attributed to the weight saving achieved, a direct result of their higher mechanical performance. Our work opens up opportunities for the use of mixed plastics in various higher value applications such that they can be diverted away from landfill or incineration, in line with the concept of circular economy.

Journal article

Eichhorn SJ, Etale A, Wang J, Berglund LA, Li Y, Cai Y, Chen C, Cranston ED, Johns MA, Fang Z, Li G, Hu L, Khandelwal M, Lee K-Y, Oksman K, Pinitsoontorn S, Quero F, Sebastian A, Titirici MM, Xu Z, Vignolini S, Frka-Petesic Bet al., 2022, Current international research into cellulose as a functional nanomaterial for advanced applications, Journal of Materials Science, Vol: 57, Pages: 5697-5767, ISSN: 0022-2461

This review paper provides a recent overview of current international research that is being conducted into the functional properties of cellulose as a nanomaterial. A particular emphasis is placed on fundamental and applied research that is being undertaken to generate applications, which are now becoming a real prospect given the developments in the field over the last 20 years. A short introduction covers the context of the work, and definitions of the different forms of cellulose nanomaterials (CNMs) that are most widely studied. We also address the terminology used for CNMs, suggesting a standard way to classify these materials. The reviews are separated out into theme areas, namely healthcare, water purification, biocomposites, and energy. Each section contains a short review of the field within the theme and summarizes recent work being undertaken by the groups represented. Topics that are covered include cellulose nanocrystals for directed growth of tissues, bacterial cellulose in healthcare, nanocellulose for drug delivery, nanocellulose for water purification, nanocellulose for thermoplastic composites, nanocellulose for structurally colored materials, transparent wood biocomposites, supercapacitors and batteries.

Journal article


Resin injection repair of composites is beneficial in circumstances where the damage has minimal fibre fracture. However, implementation to practical scenarios presents some challenges. The main aim of this work is to develop a two-dimensional reduced-order digital reconstruction, simulation and injection strategy in order to reliably conduct an efficient resin injection repair. A key objective is to ensure the repair strategy is scalable and remains practical. After establishing the basis for this method, we show a proof-of concept simulation and assess the predicted efficacy of resin injection under two injection configurations. We observe that filling efficiency is significantly improved by utilising knowledge of the reconstructed cavity to place ports and vents such that the area covered by resin flow paths are increased.

Conference paper


Empty fruit bunch (EFB) of oil palm is one of the primary wastes resulted from the production of palm oil. This work shows the potential of EFB to be produced into green fibreboard without any synthetic binder. Pulp fibres were used as binder to hold the otherwise loose efb fibres. Mechanical refining using a re-circulating colloid mill was performed to improve the binding performance of pulp fibres. This method is usually applied for improving the mechanical properties of paper. Characterisations including porosity and tension were carried out to investigate the performance of EFB fibreboards. The manufactured EFB fibreboards have the potential to be a substitute for commercial fibreboards and particleboards.

Conference paper


Dried and well-consolidated sheet of bacterial cellulose (BC) nanofibrils is a material structure that possesses high modulus and strength but is also brittle, which limits its potential in various advanced composite applications. Here, we report a simple method of enhancing the toughness of BC sheet by sizing the BC nanofibrils with poly(ethylene glycol) (PEG). This hinders interfibril hornification and facilitates large-scale BC nanofibril debonding, slippage and reorientation upon deformation. The PEG-sized BC sheets show high tensile strain-at-failure and work of fracture compared to neat BC sheet. PEG-sized BC reinforced laminated acrylic composites achieve a flatwise Charpy impact strength of up to 26 kJ m-2. This is a remarkable increase over the impact strength of neat impact-modified acrylic of only 12 kJ m-2, especially when the BC loading required to achieve this radical improvement is only 0.2 wt-%. Our study opens new paradigm in using low BC loading to achieve performance improvements suitable for high value composite applications.

Conference paper


Bacterial nanocellulose (BC) is used to create highly transparent impact resistant composites with a total light transmittance of 89 %. The composites are produced by a fast and scalable UV-polymerization-based manufacturing process. BC nanopaper is an inherently strong and fracture resistant material and is used here as reinforcement for lightweight composites aiming for ballistic protection. It is shown that creating laminated composites with alternating layers of impact-modified acrylic sheets and bacterial cellulose nanopapers can increase the impact strength by 130 % compared to the pristine impact-modified acrylic sheet. It is further noteworthy that the stacking sequence influences the impact strength strongly where a sandwich-type layup is favoured over a block-type at the same amount of cellulose nanopapers used.

Conference paper

Goosens V, Walker K, aragon S, Singh A, Senthivel V, Dekker L, Caro Astorga J, Buat M, Song W, Lee KY, Ellis Tet al., 2021, Komagataeibacter tool kit (KTK): a modular cloning system for multigene constructs and programmed protein secretion from cellulose producing bacteria, ACS Synthetic Biology, Vol: 10, Pages: 3422-3434, ISSN: 2161-5063

Bacteria proficient at producing cellulose are an attractive synthetic biology host for the emerging field of Engineered Living Materials (ELMs). Species from the Komagataeibacter genus produce high yields of pure cellulose materials in a short time with minimal resources, and pioneering work has shown that genetic engineering in these strains is possible and can be used to modify the material and its production. To accelerate synthetic biology progress in these bacteria, we introduce here the Komagataeibacter tool kit (KTK), a standardised modular cloning system based on Golden Gate DNA assembly that allows DNA parts to be combined to build complex multigene constructs expressed in bacteria from plasmids. Working in Komagataeibacter rhaeticus, we describe basic parts for this system, including promoters, fusion tags and reporter proteins, before showcasing how the assembly system enables more complex designs. Specifically, we use KTK cloning to reformat the Escherichia coli curli amyloid fibre system for functional expression in K. rhaeticus, and go on to modify it as a system for programming protein secretion from the cellulose producing bacteria. With this toolkit, we aim to accelerate modular synthetic biology in these bacteria, and enable more rapid progress in the emerging ELMs community.

Journal article

Kondor A, Santmarti A, Mautner A, Williams D, Bismarck A, Lee K-Yet al., 2021, On the BET surface area of nanocellulose determined using volumetric, gravimetric and chromatographic adsorption methods, Frontiers in Chemical Engineering, Vol: 3, Pages: 1-12, ISSN: 2673-2718

Volumetric N2 adsorption at –196 °C is generally accepted as “gold standard” for estimating the Brunauer-Emmet-Teller (BET) surface area of nanocellulose. It is unclear however, whether the BET surface area of nanocellulose obtained at such low temperatures and pressures is meaningful at an absolute sense, as nanocellulose is used at ambient temperature and pressure. In this work, a systematic evaluation of the BET surface area of nanocellulose using a highly crystalline bacterial cellulose (BC) as model nanocellulose was undertaken to achieve a comprehensive understanding of the limitations of BET method for nanocellulose. BET surface area obtained using volumetric N2 adsorption at –196 °C was compared with the BET surface area acquired from gravimetric experiments using n-octane adsorption measured using dynamic vapour sorption (DVS) and n-octane adsorption determined by inverse gas chromatography (iGC), both at 25 °C. It was found that the BET surface area calculated from volumetric N2 adsorption data was 25% lower than that of n-octane adsorption at 25 °C obtained using DVS and iGC adsorption methods. These results supported the hypothesis that the BET surface area of nanocellulose is both a molecular scale (N2 vs n-octane, molecular cross section of 0.162 nm2 vs 0.646 nm2) and temperature (–196 °C vs 25 °C) dependent property. This study also demonstrates the importance of selecting appropriate BET pressure range based on established criteria and would suggest that the room temperature gravimetric measurement is more relevant for many nanocellulose applications.

Journal article

Yang Y, Wloch D, Lee K-Y, 2021, TEMPO-oxidised nanocellulose hydrogels and self-standing films derived from bacterial cellulose nanopaper, RSC Advances: an international journal to further the chemical sciences, Vol: 11, Pages: 28352-28360, ISSN: 2046-2069

Hydrogels derived from TEMPO-oxidised cellulose nanofibrils (TOCNs) are not robust and inherently water unstable if theTOCNs are not crosslinked or coated with a water-swellable polymer. Furthermore, the manufacturing of self-standing TOCNfilms is still a challenge due to the small TOCN diameter and viscosifying effect. Here, we report the TEMPO-mediatedoxidation of bacterial cellulose (BC) nanopaper as a route to produce robust and water stable TOCN hydrogel without theneed for additional additives or crosslinking steps, as well as self-standing TOCN films without the need for vacuum filtrationor slow-drying of TOCN suspension. Pristine BC pellicle was first press-dried into a dried and well-consolidated BC nanopaper,followed by TEMPO-oxidation at various NaClO concentrations. The oxidation reaction introduced carboxylate moieties ontoexposed BC nanofibrils within the nanopaper network structure. This then led to the swelling of the nanopaper into ahydrogel. A swelling ratio of up to 100 times the original thickness of BC nanopaper was observed upon TEMPO-oxidation.The water retention value of the TEMPO-oxidised BC hydrogels was also found to increase with increasing carboxylatecontent. These TEMPO-oxidised BC hydrogels were found to be robust and water-stable, even under prolonged (>1 month)magnetic stirring in water. We further showed that high grammage self-standing TOCN films (100 g m-2) can be fabricatedas simple as press-drying a water stable TEMPO-oxidised BC hydrogels without the need of vacuum-assisted filtration orslow-drying, which is typically the rate-limiting step in the manufacturing of self-standing TOCN films.

Journal article

Caro-Astorga J, Walker KT, Herrera N, Lee K-Y, Ellis Tet al., 2021, Bacterial cellulose spheroids as building blocks for 3D and patterned living materials and for regeneration., Nature Communications, Vol: 12, Pages: 1-9, ISSN: 2041-1723

Engineered living materials (ELMs) based on bacterial cellulose (BC) offer a promising avenue for cheap-to-produce materials that can be programmed with genetically encoded functionalities. Here we explore how ELMs can be fabricated in a modular fashion from millimetre-scale biofilm spheroids grown from shaking cultures of Komagataeibacter rhaeticus. Here we define a reproducible protocol to produce BC spheroids with the high yield bacterial cellulose producer K. rhaeticus and demonstrate for the first time their potential for their use as building blocks to grow ELMs in 3D shapes. Using genetically engineered K. rhaeticus, we produce functionalized BC spheroids and use these to make and grow patterned BC-based ELMs that signal within a material and can sense and report on chemical inputs. We also investigate the use of BC spheroids as a method to regenerate damaged BC materials and as a way to fuse together smaller material sections of cellulose and synthetic materials into a larger piece. This work improves our understanding of BC spheroid formation and showcases their great potential for fabricating, patterning and repairing ELMs based on the promising biomaterial of bacterial cellulose.

Journal article

Kontturi KS, Lee K-Y, Jones MP, Sampson WW, Bismarck A, Kontturi Eet al., 2021, Influence of biological origin on the tensile properties of cellulose nanopapers, Cellulose, Vol: 28, Pages: 6619-6628, ISSN: 0969-0239

Cellulose nanopapers provide diverse, strong and lightweight templates prepared entirely from sustainable raw materials, cellulose nanofibers (CNFs). Yet the strength of CNFs has not been fully capitalized in the resulting nanopapers and the relative influence of CNF strength, their bonding, and biological origin to nanopaper strength are unknown. Here, we show that basic principles from paper physics can be applied to CNF nanopapers to illuminate those relationships. Importantly, it appeared that ~ 200 MPa was the theoretical maximum for nanopapers with random fibril orientation. Furthermore, we demonstrate the contrast in tensile strength for nanopapers prepared from bacterial cellulose (BC) and wood-based nanofibrillated cellulose (NFC). Endemic amorphous polysaccharides (hemicelluloses) in NFC act as matrix in NFC nanopapers, strengthening the bonding between CNFs just like it improves the bonding between CNFs in the primary cell wall of plants. The conclusions apply to all composites containing non-woven fiber mats as reinforcement.

Journal article

Gaduan AN, Solhi L, Kontturi E, Lee K-Yet al., 2021, From micro to nano: polypropylene composites reinforced with TEMPO-oxidised cellulose of different fibre widths, Cellulose, Vol: 28, Pages: 2947-2963, ISSN: 0969-0239

TEMPO-oxidised cellulose fibres are often explored as nano-reinforcement for polymers. However, it is unclear whether micrometre-sized TEMPO-oxidised cellulose fibres also possess similar reinforcing potential. In this work, we report the mechanical response of polypropylene (PP) composites reinforced with TEMPO-oxidised cellulose (TOC) of different fibre widths. Micrometre-sized TOC fibres (TOCF) containing sodium carboxylate (TOCF-Na) and free hydroxyl (TOCF-H) groups, as well as nano-sized TOC nanofibrils (TOCN) were produced from dissolving pulp and incorporated into PP matrix via melt-extrusion. It was found that model PP composites containing micrometre-sized TOCF-Na and TOCF-H possessed the highest tensile modulus of up to 2.5 GPa; 40% improvement over neat PP and 30% increase over PP/TOCN composite. No significant differences in the tensile strength of PP/TOCF-Na and PP/TOCF-H composites were observed when compared to neat PP. The incorporation of nano-sized TOCN into PP however, led to a 6% decrease in tensile strength. Single-edge notched beam fracture toughness test further showed that PP/TOCN composite possessed the lowest fracture toughness of 2.52 MPa m1/2; a decrease of 18% over PP reinforced with micrometre-sized TOCF-Na and TOCF-H. Our study shows that micrometre-sized TOCFs serve as better reinforcement for polymers compared to nano-sized TOCN. This is attributed to the better dispersion of TOCF in the PP matrix. Furthermore, the presence of surface microfibrillation on TOCFs also enhanced the quality of the TOCF-PP interface through mechanical interlocking and local stiffening of the PP matrix.

Journal article

Santmarti A, Tammelin T, Lee K-Y, 2020, Prevention of interfibril hornification by replacing water in nanocellulose gel with low molecular weight liquid poly(ethylene glycol), Carbohydrate Polymers, Vol: 250, Pages: 1-9, ISSN: 0144-8617

Nanocellulose is typically stored and transported as a gel with a nominal solid content of up to 5 wt.-% to avoid interfibril hornification, i.e. the formation of irreversible hydrogen bonds between adjacent nanocellulose upon drying, which makes nanocellulose not cost-effective. In this work, we report the use of low molecular weight liquid poly(ethylene glycol) (PEG-200) as a replacement for the water phase in nanocellulose aqueous gel. Our results indicated that nanocellulose can be stored in PEG-200 at a solid content of up to 70 wt.-% without interfibril hornification, even when exposed to the ambient environment. This is due to the low vapour pressure and high boiling point of PEG-200. ATR-FTIR and ζ-potential measurements confirmed that PEG-200 can be easily washed out from the nanocellulose as PEG-200 is water miscible. Using PEG-200 as a replacement for the water phase in nanocellulose aqueous gel could improve the cost-efficiency of nanocellulose storage and transportation. The tensile properties of the cellulose nanopaper prepared from the various never-dried and once-dried nanocellulose are also discussed in this work.

Journal article

Vilchez V, Dieckmann E, Tammelin T, Cheeseman C, Lee K-Yet al., 2020, Upcycling Poultry Feathers with (Nano)cellulose: Sustainable Composites Derived from Nonwoven Whole Feather Preforms, ACS Sustainable Chemistry & Engineering, Vol: 8, Pages: 14263-14267, ISSN: 2168-0485

Journal article

Santmarti A, Liu HW, Herrera N, Lee K-Yet al., 2020, Anomalous tensile response of bacterial cellulose nanopaper at intermediate strain rates, Scientific Reports, Vol: 10, ISSN: 2045-2322

Nanocellulose network in the form of cellulose nanopaper is an important material structure and its time-dependent mechanical response is crucial in many of its potential applications. In this work, we report the influences of grammage and strain rate on the tensile response of bacterial cellulose (BC) nanopaper. BC nanopaper with grammages of 20, 40, 60 and 80 g m−2 were tested in tension at strain rates ranging from 0.1% s−1 to 50% s−1. At strain rates ≤ 2.5% s−1, both the tensile modulus and strength of the BC nanopapers stayed constant at ~ 14 GPa and ~ 120 MPa, respectively. At higher strain rates of 25% s−1 and 50% s−1 however, the tensile properties of the BC nanopapers decreased significantly. This observed anomalous tensile response of BC nanopaper is attributed to inertial effect, in which some of the curled BC nanofibres within the nanopaper structure do not have enough time to uncurl before failure at such high strain rates. Our measurements further showed that BC nanopaper showed little deformation under creep, with a secondary creep rate of only ~ 10–6 s−1. This stems from the highly crystalline nature of BC, as well as the large number of contact or physical crosslinking points between adjacent BC nanofibres, further reducing the mobility of the BC nanofibres in the nanopaper structure.

Journal article

Song W, Magid A, Li D, Lee K-Yet al., 2020, Application of recycled carbon-fibre-reinforced polymers as reinforcement for epoxy foams, JOURNAL OF ENVIRONMENTAL MANAGEMENT, Vol: 269, ISSN: 0301-4797

Journal article

Gregory GL, Sulley GS, Carrodeguas LP, Chen TTD, Santmarti A, Terrill NJ, Lee K-Y, Williams CKet al., 2020, Triblock polyester thermoplastic elastomers with semi-aromatic polymer end blocks by ring-opening copolymerization, Chemical Science, Vol: 11, Pages: 6567-6581, ISSN: 2041-6520

Thermoplastic elastomers benefit from high elasticity and straightforward (re)processability; they are widely used across a multitude of sectors. Currently, the majority derive from oil, do not degrade or undergo chemical recycling. Here a new series of ABA triblock polyesters are synthesized and show high-performances as degradable thermoplastic elastomers; their composition is poly(cyclohexene-alt-phthalate)-b-poly(ε-decalactone)-b-poly(cyclohexene-alt-phthalate) {PE–PDL–PE}. The synthesis is accomplished using a zinc(II)/magnesium(II) catalyst, in a one-pot procedure where ε-decalactone ring-opening polymerization yielding dihydroxyl telechelic poly(ε-decalatone) (PDL, soft-block) occurs first and, then, addition of phthalic anhydride/cyclohexene oxide ring-opening copolymerization delivers semi-aromatic polyester (PE, hard-block) end-blocks. The block compositions are straightforward to control, from the initial monomer stoichiometry, and conversions are high (85–98%). Two series of polyesters are prepared: (1) TBPE-1 to TBPE-5 feature an equivalent hard-block volume fraction (fhard = 0.4) and variable molar masses 40–100 kg mol−1; (2) TBPE-5 to TBPE-9 feature equivalent molar masses (∼100 kg mol−1) and variable hard-block volume fractions (0.12 < fhard < 0.4). Polymers are characterized using spectroscopies, size-exclusion chromatography (SEC), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). They are amorphous, with two glass transition temperatures (∼−51 °C for PDL; +138 °C for PE), and block phase separation is confirmed using small angle X-ray scattering (SAXS). Tensile mechanical performances reveal thermoplastic elastomers (fhard < 0.4 and N > 1300) with linear stress–strain relationships, high ultimate tensile strengths (σb = 1–5 MPa), very high elongations at break (&ep

Journal article

Mautner A, Nawawi WMFW, Lee K-Y, Bismarck Aet al., 2020, High porosity cellulose nanopapers as reinforcement in multi-layer epoxy laminates, Composites Part A: Applied Science and Manufacturing, Vol: 131, Pages: 1-9, ISSN: 1359-835X

Utilizing high-performance cellulose nanopapers as 2D-reinforcement for polymers allows for realizing high-loading-fraction (80 vol-%), high-performance (strength > 150 MPa, modulus > 10 GPa) laminated nanopaper reinforced epoxy composites. Such cellulose nanopapers are inherently dense, which renders them difficult to be impregnated with the epoxy-resin. High-porosity nanopapers facilitate better resin impregnation, truly utilizing the properties of single cellulose nanofibres instead of the nanofibre network. We report the use of high-porosity (74%) but low strength and modulus bacterial cellulose (BC) nanopapers, prepared from BC-in-ethanol dispersion, as reinforcement for epoxy-resin. High-porosity nanopapers allowed for full impregnation of the BC-nanopapers with epoxy-resin. The resulting BC-reinforced epoxy-laminates possessed high tensile modulus (9 GPa) and strength (100 MPa) at a BC loading of 30 vol-%, resulting from very low void-fraction (3 vol-%) of these papregs compared to conventional nanopaper-laminates (10+ vol.-%). Better resin impregnation of less dense nanocellulose networks allowed for maximum utilization of stiffness/strength of cellulose nanofibrils.

Journal article

Nawawi WMFW, Lee K-Y, Kontturi E, Bismarck A, Mautner Aet al., 2020, Surface properties of chitin-glucan nanopapers from Agaricus bisporus, International Journal of Biological Macromolecules, Vol: 148, Pages: 677-687, ISSN: 0141-8130

The structural component of fungal cell walls comprises of chitin covalently bonded to glucan; this constitutes a native composite material (chitin-glucan, CG) combining the strength of chitin and the toughness of glucan. It has a native nano-fibrous structure in contrast to nanocellulose, for which further nanofibrillation is required. Nanopapers can be manufactured from fungal chitin nanofibrils (FChNFs). FChNF nanopapers are potentially applicable in packaging films, composites, or membranes for water treatment due to their distinct surface properties inherited from the composition of chitin and glucan. Here, chitin-glucan nanofibrils were extracted from common mushroom (Agaricus bisporus) cell walls utilizing a mild isolation procedure to preserve the native quality of the chitin-glucan complex. These extracts were readily disintegrated into nanofibre dimensions by a low-energy mechanical blending, thus making the extract dispersion directly suitable for nanopaper preparation using a simple vacuum filtration process. Chitin-glucan nanopaper morphology, mechanical, chemical, and surface properties were studied and compared to chitin nanopapers of crustacean (Cancer pagurus) origin. It was found that fungal extract nanopapers had distinct physico-chemical surface properties, being more hydrophobic than crustacean chitin.

Journal article

Sulley GS, Gregory GL, Chen TTD, Carrodeguas LP, Trott G, Santmarti A, Lee K-Y, Terrill NJ, Williams CKet al., 2020, Switchable catalysis improves the properties of CO2-derived polymers: poly(cyclohexene carbonate-b-epsilon-decalactone-b-cyclohexene carbonate) adhesives, elastomers, and toughened plastics, Journal of the American Chemical Society, Vol: 142, Pages: 4367-4378, ISSN: 0002-7863

Carbon dioxide/epoxide copolymerization is an efficient way to add value to waste CO2 and to reduce pollution in polymer manufacturing. Using this process to make low molar mass polycarbonate polyols is a commercially relevant route to new thermosets and polyurethanes. In contrast, high molar mass polycarbonates, produced from CO2, generally under-deliver in terms of properties, and one of the most widely investigated, poly(cyclohexene carbonate), is limited by its low elongation at break and high brittleness. Here, a new catalytic polymerization process is reported that selectively and efficiently yields degradable ABA-block polymers, incorporating 6–23 wt % CO2. The polymers are synthesized using a new, highly active organometallic heterodinuclear Zn(II)/Mg(II) catalyst applied in a one-pot procedure together with biobased ε-decalactone, cyclohexene oxide, and carbon dioxide to make a series of poly(cyclohexene carbonate-b-decalactone-b-cyclohexene carbonate) [PCHC-PDL-PCHC]. The process is highly selective (CO2 selectivity >99% of theoretical value), allows for high monomer conversions (>90%), and yields polymers with predictable compositions, molar mass (from 38–71 kg mol–1), and forms dihydroxyl telechelic chains. These new materials improve upon the properties of poly(cyclohexene carbonate) and, specifically, they show good thermal stability (Td,5 ∼ 280 °C), high toughness (112 MJ m–3), and very high elongation at break (>900%). Materials properties are improved by precisely controlling both the quantity and location of carbon dioxide in the polymer chain. Preliminary studies show that polymers are stable in aqueous environments at room temperature over months, but they are rapidly degraded upon gentle heating in an acidic environment (60 °C, toluene, p-toluene sulfonic acid). The process is likely generally applicable to many other lactones, lactides, anhydrides, epoxides, and heterocumulenes and sets the s

Journal article

Santmarti A, Zhang H, Lappalainen T, Lee K-Yet al., 2020, Cellulose nanocomposites reinforced with bacterial cellulose sheets prepared from pristine and disintegrated pellicle, Composites Part A: Applied Science and Manufacturing, Vol: 130, Pages: 1-9, ISSN: 1359-835X

BC sheets can be prepared in two forms: direct press-drying of the as-synthesised BC pellicle or disintegrating the BC pellicle to create a homogenous BC-in-water suspension prior to producing the BC sheet. We found that BC sheet prepared from direct press-drying of pristine pellicle was more homogeneous due to its better BC network formation and possessed higher specific surface area (46 g m−2), better resin impregnation and mechanical properties compared to its disintegrated pellicle counterpart (21 g m−2). BC-poly(acrylated epoxidised soybean oil) (polyAESO) nanocomposites consisting of BC sheet prepared from pristine pellicle was optically transparent whilst BC-polyAEO nanocomposites consisting of BC sheet prepared from disintegrated pellicle was opaque. Whilst the tensile properties of BC-polyAESO nanocomposites from pristine pellicle were higher, the fracture toughness of BC-polyAESO composite consisting of BC sheet from disintegrated pellicle was better. The lack of resin impregnation in BC-polyAESO from disintegrated pellicle led to a laminated structure, which utilised the fracture toughness of BC sheet effectively.

Journal article

Nawawi WMFBW, Jones M, Murphy RJ, Lee K-Y, Kontturi E, Bismarck Aet al., 2020, Nanomaterials derived from fungal sources-is It the new hype?, Biomacromolecules, Vol: 21, Pages: 30-55, ISSN: 1525-7797

Greener alternatives to synthetic polymers are constantly being investigated and sought after. Chitin is a natural polysaccharide that gives structural support to crustacean shells, insect exoskeletons, and fungal cell walls. Like cellulose, chitin resides in nanosized structural elements that can be isolated as nanofibers and nanocrystals by various top-down approaches, targeted at disintegrating the native construct. Chitin has, however, been largely overshadowed by cellulose when discussing the materials aspects of the nanosized components. This Perspective presents a thorough overview of chitin-related materials research with an analytical focus on nanocomposites and nanopapers. The red line running through the text emphasizes the use of fungal chitin that represents several advantages over the more popular crustacean sources, particularly in terms of nanofiber isolation from the native matrix. In addition, many β-glucans are preserved in chitin upon its isolation from the fungal matrix, enabling new horizons for various engineering solutions.

Journal article

Jiang Q, Lee K, Bismarck A, 2020, Foam templating: A greener route to porous polymers, ACS Symposium Series, Pages: 99-118

A simple kitchen mixer and skills to whip cream can be useful to manufacture highly functional polymer foams with control over their structures. In the 1930s, researchers began to whip or inject gas into monomers or polymer suspensions to produce liquid foams, which served as templates to be solidified to polymer foams. Besides the “simplicity” of the foam templating method, its actual advantage as compared to widely used blown polymer foams is the nonessential need of physical and chemical blowing agents, resulting in a lower raw material cost, less involved chemistry, lower safety and health risk during production and a reduced impact on the environment. Compared to other templating methods, such as emulsion templating, which require sacrificial materials serving as templates, liquid foams with bubbles as templates are superior from a material processing perspective because they require no further materials or energy for template removal. A challenging step in foam templating is to create a stable liquid foam containing building blocks for subsequent solidification; when using air as an internal phase, the choice of materials in the liquid phase to create a stable colloidal system is restricted. In this chapter, we review previous work on foam templating with a focus on porous materials produced therefrom, including macroporous thermoplastic, thermosetting polymers, hydrogels, biobased materials and polymer composites. We aim to show that foam templating is a greener than any other templating methods, such as emulsion templating and particulate leaching, and versatile foaming process and to encourage researchers to conduct both fundamental and applied research to push the boundaries of this technology further.

Book chapter

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